GB579725A - Improvements in or relating to pulse generating thermionic valve apparatus - Google Patents

Abstract

579,725. Valve generating circuits. BLUMLEIN, A. D., and WHITE, E. L. C. Jan. 27, 1940, No. 1689. [Class 40 (v)] High voltage impulses of short duration relative to the intervals between them are generated across an inductance coil in the anode circuit of a valve by applying a negative pulse to the grid of the valve. The coil may be associated with a mis-terminated time delay network giving a reflected pulse of opposite polarity. The impulses may be applied to the anode circuits of radio frequency amplifiers or oscillators to give short bursts of radiofrequency energy for use in locating reflecting objects such as aircraft. As shown in Fig. 1 (Prov.) the impulses are generated across a coil 8 in the anode circuit of a valve 13 when this valve is suddenly rendered non-conducting by impulses applied to its grid. The high voltage generated is applied to the anodes of push-pull radio frequency amplifiers or oscillators 3, causing the emission of a short burst of waves in the output circuit 7. Lower voltages are simultaneously applied to the screen-grids and control grids of the valves 3 from tappings on the coil 8, or separate means may be provided for this purpose. Oscillation of the coil 8 after the initial surge is prevented by connecting a resistance or a diode valve 15 across the whole or part of the coil. A low tapping on the coil 8 may be connected to the grid of a valve 16, the anode of which is connected to the grid of the valve 13 to ensure that the latter valve is held in the non-conducting state for the pulse period, and is rendered conducting to act as a damping resistance should the coil 8 oscillate. The control pulses applied to the grid of the valve 13 are preferably of saw-tooth form, and may be generated by applying rectangular pulses through a resistance 17 and diode 19 to a condenser 18, Fig. 2 (Prov.). The condenser is charged quickly through the diode valve, and discharges slowly through a high resistance 20, and the saw-tooth wave is taken off through a condenser 21 and leak resistance 22. The modification shown in Fig. 1 (Comp.) employs four valves 13 connected in parallel, and the coil 8 is shunted to earth by a number of condensers to form a delay network, which, by reflection at its closed outer end, provides a voltage pulse having a duration equal to twice the time delay. The sharpness of the voltage impulse is improved by connecting inductances 26a, 26b, 26c, in the anode leads. A resistance 29 and a parallel resonant circuit 30, 31 may be connected in the screen grid leads of the valves 13, to reduce the power dissipated in these valves during the period when they are conducting.